My custom pcb cannot reach the power specifications of the nucleo

[Aurélien f]

Posted on November 16, 2017 at 13:06

Hello,

On my nucleo-l073 board, my software can run in stop mode and consumes only 3uA. I decided to make my own PCB but i can't figure out why the consumption can't reach 3uA. Actually, i'm running around 25uA with the same software. I'm using a stencil and a reflow oven to solder the components (T-962) and the solder paste is a Sn63 Pb37. I'm making the pcb by PCBway and i take the cheapest quality (5$ for 10 pieces : TG 130-140 (i don't what it means)), do you think it could come from that ?

I have also noticed when i put my finger directly on the stm32, consumption often decreases.

If you have any ideas, please feel free to share

Thank you in advance.

Edit : I join in attached file my schematic and my PCB (the ground planes are not displayed)

Best regards,

Aur�lien

#stop-mode #low-power #stm32 #pcb #nucleo-l073rz #pcbway

[S.Ma]

Posted on November 16, 2017 at 14:42

Is it the same package? More GPIOs? Are they polarized properly? Oscillators are all same and off? Reset signal? If there are some pull-ups and pull-down, you could have few uA there. Example would be I2C Pull-ups and SW is stopped while I2C bus lines were used and are low level.

[Aurélien f]

Posted on November 16, 2017 at 15:40

Thank you very much for the reply.

No, it is not the same package, i'm using a stm32l073cbt6 (48pin) whereas it is a 64pin on nucleo-l073.

To test, on my own board, i'm only soldering the stm32, the pull down resistor (10k) on boot0 and all decoupling capacitors.

I m also loading the same firmware on my nucleo board or my custom board (so all peripherals are deactivated, only RTC (running on LSI) is on and ADC).

[Antonio Vilei]

Posted on November 17, 2017 at 16:22

Hi Aurélien,

since the package and the pinout is different, maybe there are some slight differences in the way the GPIOs have been configured. Did you check whether all the pins that you don't need are actually configured as analog with no pull on your custom board?

Best regards,

Antonio

[Aurélien f]

Posted on November 22, 2017 at 16:10

Hello,

I have noticed when i connect the pin 2 (PC13) to the ground, my current consumption is around 2.9uA (exactly what i want and this is exactly the same current consumption as the nucleo board). But it is not indicated in the datasheet that this pin should be put to the ground and on the nucleo board, this pin is not put to the ground. 

Did i miss something in the datasheet ? Or Am i doing something wrong ?

I have tested this on three of my custom boards and in the three cases, the current consumption falls down to 2.9uA.

Regards,

Aurélien

[alexandre239955_stm1]

Posted on November 23, 2017 at 13:11

As the datasheet says, PC13 is used for RTC_TAMP1/RTC_TS/RTC_OUT/WKUP2, and you said previously that you are using the RTC. Try to enable the pull-down on this pin.

[Aurélien f]

Posted on November 23, 2017 at 15:33

Hi,

Thank you for the reply. 

I tried what you proposed but unfortunatly it didn't change anything. I have also tried to not use RTC but without success, i'm still having this extra current consumption if i don't connect PC13 to the ground !

Regards,

Aurélien

[Brow Joey]

Posted on November 23, 2017 at 07:47

I've heard about pcbway service.

I've recently used Seeed Studio's

https://www.seeedstudio.com/fusion_pcb.html

to try them out - I'm very impressed with them, it was the lowest overall price I could find anywhere but still had excellently short manufacturing and shipping time (I paid for DHL).

[Michael Stevens]

Posted on November 27, 2017 at 16:46

I'm still sorting out some of the intricacies of STM32s, how the parts come out of reset, and the software framework, but I suspect, based on what you've said thus far, that PC13 is still configured as an input.  Even though the actual peripheral functionality may be deactivated, if the input buffer is still on, leaving this floating would result in internal oscillations and shoot-through currents in the input totem.  

Looking at the Nucleo schematic, PC13 is used by the the blue pushbutton and has a PU to VDD, so it's being held in a known logic state.  If you cut the solder bridge, you would probably see similar current consumption on the Nucleo.

[Aurélien f]

Posted on November 28, 2017 at 13:51

Hi,

Exactly, when i cut the solder bridge SB17, i have the same bahavior with unregular current consumption, even if i set this pin with an internal pull up or pull down ...

So my question is : is it preferable to put a pull up with a 100k resistor or directly connected to the ground ?

Regards,

Aurélien

[Michael Stevens]

Posted on November 29, 2017 at 18:53

Hi Aurélien,

Peculiar... I would whitewire a PU to VDD and see what happens. 

If the internal PU or PD are enabled and no external PU or PD is present, you should only see additional currents that correlate to the IO leakage currents as specified in the datasheet unless you have another path for current to flow.  If you enable both the PU and PD, then the current would be considerably higher than just the IO leakage.

How is PC13 configured by firmware?